1. Field of the Invention
The present invention relates to the transmission of a multiplicity of signals between an electronic assembly and a module situated at a location remote from the electronic assembly, some of the signals being transmitted from the electronic assembly to the module and the remaining signals being transmitted in the opposite direction.
2. Description of the Prior Art
In an arrangement of the type described above, the electronic assembly can be a base station, for example, in which the signals that are to be transmitted to the module situated remote from the base station are produced and in which there takes place a signal processing of the signals communicated by the module takes place. The module can contain, for example, a module for converting the frequency of one or more signals, and can be fashioned, for example, as a frequency converter.
A module for frequency conversion, hereinafter designated a frequency converter, in which the frequency of a radio-frequency (RF) signal is converted to an intermediate frequency position, is generally supplied with a signal of a local oscillator (LO), called an LO signal. Correspondingly, the frequency converter requires, apart from the input line for the RF signal, a line for the LO signal and a line for the intermediate frequency signal (IF signal).
Such a frequency converter is attached, for example, to the tip of an antenna mast, where it receives RF signals from the surrounding environment that are to be converted into an IF signal. Due to atmospheric influences, however, a thermal drift of the frequency of the LO signal may occur if the local oscillator is integrated into the frequency converter. Alternatively, it is possible for example to transmit a highly stable LO signal from a remotely positioned local oscillator to the frequency converter via a cable connection. The local oscillator is ideally seated in or adjacent to the electronic assembly in which the IF signal, i.e. the output signal of the frequency converter, is also further processed. Correspondingly, the IF signal is also conducted via a cable connection to the electronic assembly positioned remote from the frequency converter.
If n channels, i.e. n RF signals having n generally different frequencies, are to be converted into n different IF bands, n different LO frequencies and n individual IF output lines are generally required. Accordingly, for n channels 2n lines must be provided—again, apart from the input lines for the RF signals that are to be converted.
Such a frequency converter for the conversion of n channels is used for example in magnetic resonance tomography (MRT) when surface or head coils having, for example, 128 channels are used. Correspondingly, for the LO and the IF signals 2×128=256 lines extend between the frequency converter of the coil and the electronic assembly in which, in this application situation, at least one local oscillator, as well as an analog and a digital electronics unit, are housed for post-processing the IF signal. The signal detected by the coil is first amplified using a low-noise preamplifier and is then supplied to the frequency converter. For an optimal signal-to-noise ratio, the electrical connections between the pickoff point of the signals detected by the coil and the preamplifier should be as short as possible. If, however, the preamplified signals are first led out from the coil via longer lines and then supplied to the frequency converter, then due to the identical frequency there would be the danger of a feedback effect on the coil, accompanied by the production of unwanted oscillations and/or significant changes in frequency response. The frequency converter is therefore ideally situated as close as possible to the output of the preamplifier, and is typically integrated into the coil housing.
In addition to the e.g. 256 signals that have to be transmitted between the electronic assembly and the frequency converter, in the case of the surface coil or the head coil there is a further signal for the transmit/receive changeover of the surface coil, known as the PIN diode signal or PIN signal. For this PIN signal, in addition to the lines for the LO and IF signals, a further line is required between the surface coil and the electronic assembly.
In order to exclude for example disturbing influences due to RF excitation pulses or gradient fields to the greatest possible extent, for the example of MRT the electronic assembly is also standardly situated remotely from the frequency converter. Thus, a correspondingly large number of lines must be provided for the transmission of the LO, IF, and PIN signals.
The provision of such a large number of lines for the conversion of n channels is associated with a high outlay and corresponding costs.
In DE 101 48 467 A1, a number of magnetic resonance signals (MR signals) of a surface coil are mixed in various RF bands, and these RF bands are transmitted via a readout line. In addition, the direct voltage for the power supply, various control signals, and a synchronization frequency are transmitted via this line. The LO signals required for the mixing up are produced locally in the electronics of the surface coil, and are synchronized if warranted. However, the correspondingly necessary electronics outlay entails a large space requirement. Above all, however, the electronics causes a relatively high power loss, which in addition occurs in the vicinity of the patient and therefore can cause an unnecessary rise in the patient's temperature. The direct voltage for the supply of power to the electronics is also transmitted via this line, while for the transmission of PIN signals an additional electronics unit is required, entailing an additional space requirement and higher power loss.
As a generalization, and for better illustration of the fact that the module or frequency converter is situated remotely from the further signal processing, the electronic assembly in which, inter alia, the signal processing takes place is also designated a “base station,” and the frequency converter is designated a “satellite.” In the case of MRT, the satellite would then be a surface coil or a surface coil array, and the base station would be the assembly in which at least the further processing of the IF signals takes place.